An inhibitory reflex may be envoked by activating sensory endings in the left ventricle either by chemical activation with veratridine (Bezold-Jarisch reflex) or by stretch of the left ventricle (LV). A previously unrecognized coronary artery vasodilation has recently been shown to be part of this reflex. Furthermore, a preferential distribution of left ventricular receptor activity to the posterior inferior wall of the LV is present in dogs. We assume that there is a coordination of the elements of neural balance on coronary artery blood flow (Alpha and Beta adrenergic, and parasympathetic). We hypothesize that the medullary center receives sensory inputs from receptors distributed throughout the cardiac ventricles and is able to identify the region of the ventricular tissue and receptor type which gave rise to each. The center considers available hemodynamic information and directs a coordinated response which includes appropriate regional cardiac changes. We will test two corollaries (C) of this hypothesis in a resting unanesthetized canine model chronically instrumented to measure myocardial segment lenth and blood flow (Doppler flowprobes) to regions perfused by the right (RCA), left anterior descending (LAD), septal, circumflex (CX), and marginal coronary arteries during artial pacing. Chronic catheters will allow selective injection into proximal RCA, LAD, or CX. The three ventricular regions - right ventriculr free wall (RVFW), septum (S), and LV free wall (LVFW) were chosen because their anatomical and functional contract make regional differences in neurohumoral control likely. C #1 - The changes in coronary artery blood flow caused by the Bezold-Jarisch reflex vary regionally depending on the location of the ventricular receptors stimulated. This will be tested by noting the reflex effects of selective (RCA, LAD, or CX) veratridine injection on regional blood flow (RVFW, S, LVFW) in the presence of Alpha and Beta adrenergic receptor blockage. C #2 - Resting coronary artery Alpha and Beta adrenergic and cholinergic activity varies regionally in the cardiac ventricles. This will be tested by noting the effects of selective blockade or injection (RCA, LAD, or CX) of agonist (Beta or cholinergic) in presence of blockage of competing neurohumoral influences on regional blood flow (RVFW, S, LVFW). An understanding of the regional balance of neural influences in the resting situation is essential to an appreciation of how these factors help to achieve a blood flow appropriate to various regions of the ventriculr myocardium. This understanding is fundamental to any investigation into derangements of these forces such as those resulting in coronary artery spasm.